The present invention relates to optical fiber which has a polymer core, and cladding of polymer which has an index of refraction lower than that of the core.
Optical fibers are well known in the art for transmission of light along a length of filament by multiple internal reflections of light. Great care is taken to minimize light losses due to absorption and scattering along the length of the filament, so that light applied to one end of the optical filamentary material is efficiently transmitted to the opposite end of the material. The light transmitting portion or core of the optical filamentary material is surrounded by cladding having an index of refraction lower than that of the core, so as to achieve total internal reflection along the length of the filament. This cladding is normally chosen to be transparent since an opaque cladding tends to absorb or scatter light.
An important consideration in formation of optical fibers is minimization of any factor which increases the attenuation of transmitted light within such a fiber.
Optical fibers which consist wholly of inorganic glasses, or which have an inorganic glass core surrounded by a thermoplastic or thermosetting polymer, or which consist wholly of thermoplastic polymer, are all known in the art. Those having inorganic glass cores, especially fused silica cores, exhibit high light transmission, i.e., low attenuation of transmitted light, but are relatively easily damaged by fracture if bent to too small a radius of curvature or otherwise abused; they can be protected by use of a shielding layer, but this adds undesired bulk, weight and expense, and nevertheless does not always enable the fiber to be used in situations where bending to a small radius of curvature is helpful or required. The all-plastic fibers are less subject to fracturing, but have the deficiency that they more strongly attenuate light passing therethrough. The present invention is directed to improving the capability of all-plastic optical fibers to transmit light. It is also directed to a process for making high quality polymers of methyl methacrylate which are preeminently suitable for the core component of optical fibers.